1. Field of the Invention
This invention relates to the field of molds for making foam products, and more particularly to the field of non-stick molds for making polyurethane foam products, such as disposable earplugs.
2. Description of the Prior Art
Molded polyurethane foam products are usually formed in a mold having one or more cavities provided therein to give the foamed product its molded shape. In normal operation, the foam precursor Components are placed in each mold cavity and a cover is applied to the mold. The foam components react to form the foam. As the foam expands, it conforms to the shape of the mold cavity,, thereby forming a foamed product of a desired shape.
A problem generally encountered when forming molded foam products is the inability of the molded product to be easily removed from the mold. Typically, mold release agents must be applied to the mold cavities prior to the introduction of the precursor foam components. These mold release agents permit the molded foam product to be easily removed from the mold.
Although the mold release agent may assist the removal of the molded foam product, the agent may create undesirable side effects. The mold release agent may react with either the foam components or the molded foam product or leach into the molded foam product and affect the properties of the product. When the foam product has been selected because of desirable properties, the leaching of the mold release agent into the product may substantially change those desired properties. Such is true in the case of molded foam earplugs in which the mold release agent may impart undesirable plasticization effects to the earplug. Consequently, there is a need for a mold which will permit the easy removal of a foamed product without the need for mold release agents.
Repeated use of a mold may result in deterioration of the mold cavity. When that occurs the mold must be replaced. Sometimes, the mold is scratched during use, which scratches frequently occur near the edge of the mold cavity. If a scratch occurs at the edge of a mold cavity, the desired seal between the top and bottom of the mold is broken but the mold cavity is otherwise useful. Yet, the absence of a proper seal makes the mold ineffective. Such a mold must be repaired or destroyed. Many molds are quite expensive. There is a need for a mold which can be replaced inexpensively and which has the strength, compatibility and other desirable properties of molds currently in use. There is also a need for a mold having an elastomeric cap for each mold cavity which will conform to the edge of the cavity and seal any scratches that are present on the edge.